A microwave oven as a typical microwave heating apparatus supplies a microwave radiated from a magnetron as a typical microwave generating unit, into a metal heating chamber to inductively heat a heating object in the heating chamber.
In recent years, a highly convenient product has been put into practical use, where a bottom surface is made flat and a food can be arranged both left and right to heat two foods. However, if a frozen food and a room-temperature food are heated at the same time as the two foods, for example, the room-temperature food will be finished earlier. Therefore, in order to finish two foods at the same time, a food at a lower temperature should be intensively heated. In such a case, a function is required that enables local intensive heating instead of uniformly heating the entire heating chamber. This function can be achieved by those having a rotating antenna with a rotation shaft at substantially the center of a heating chamber bottom surface so that the stop position control of the rotating antenna is provided based on inside temperature distribution detected by an infrared sensor (see, e.g., Patent Documents 1 and 2).
The rotating antenna is designed to have high outward directivity of microwave with respect to the rotation shaft so that when the rotating antenna is stopped toward a food on the lower temperature when cooking two foods, the food can be intensively heated. Waveguide-structure antennas 1, 11, 21 as shown in FIGS. 34 to 37 are known as rotating antennas excellent particularly in local heating performance (see Patent Documents 1 and 2). FIGS. 34 and 35 depict a waveguide-structure antenna 1 described in Patent Document 1. FIGS. 36 and 37 depict waveguide-structure antennas 11 and 21, respectively, described in Patent Document 2.
The waveguide-structure antennas 1, 11, 21 have box-shaped waveguide structures 3, 13, 23 configured to surround coupling shafts 2, 12, 22 to which microwaves are supplied. Wall surfaces forming the waveguide structures 3, 13, 23 have upper wall surfaces 4, 14, 24 connected to the coupling shafts 2, 12, 22, and side wall surfaces 5a to 5c, 15a to 15c, 25a to 25c around the upper wall surfaces 4, 14, 24 closing the structures in three directions. The wall surfaces forming the waveguide structures 3, 13, 23 also have flanges 7, 17, 27 which are formed on the outside of the side wall surfaces 5a to 5c, 15a to 15c, 25a to 25c and in parallel with heating chamber bottom surfaces 6, 16, 26 via a slight gap. The wall surfaces form distal-end opening parts 8, 18, 28 widely opened only at a distal end toward one direction. In such a configuration, a large portion of microwaves is radiated only from the distal-end opening parts 8, 18, 28 to enhance the directivity of microwaves toward the distal-end opening parts 8, 18, 28 from the coupling shafts 2, 12, 22. Such a microwave supply system is rotated around the coupling shafts 2, 12, 22 and therefore may also be referred to as a rotating waveguide system.